This exception wise might be the case but, the cost to performance is probably just less for some senior folks compared to up and coming new people. For instance if i have 10+ year employee who has received 3% cost of living raises + additional performance raises they likely have a cost/performance ratio worse than the A player with 5 years experience who wants to move up. I can promote them for a bump in salary and have someone who hasn't accumulated as much cost overtime with a similar performance. I reduced capacity, improved moral for an A player and cut cost in one decision. There would also be minimal impact moral wise to the remaining organization by hiring within. That's just my take though and I am no authority in the topic.